TWI911445B - Thermally conductive silicone compounds and their cured products - Google Patents

Abstract

This invention provides a thermally conductive silicone composition. It forms a crack-free and void-free hardened material with good thermal conductivity. The thermally conductive silicone composition comprises the following components. (A) Organic polysiloxane, having a kinematic viscosity of 10~1,000,000 ^mm² /s at 25°C, and having two or more aliphatic unsaturated hydrocarbons bonded to silicon atoms in one molecule; (B) Organic hydrogen polysiloxane, having two or more hydrogen atoms bonded to silicon atoms in one molecule; (C) Gallium and/or gallium alloys, having a melting point of -20~70°C; (D) Thermally conductive filler, having an average particle size of 0.1~100 µm; (E) Platinum group metal catalyst; (F) Palladium powder; (G-1) Organic polysiloxane, represented by the following general formula (1). (In formula (1), ^R1 is independently an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms that does not have aliphatic unsaturated bonds, and ^R2 is independently an alkyl, alkenyl, or acetyl group. In addition, a is an integer from 5 to 100, and b is an integer from 1 to 3.)

Description

Thermally conductive silicone compounds and their cured products

This invention relates to thermally conductive silicone compounds and their cured forms.

Heat-generating electronic components packaged on printed circuit boards, such as CPUs and other IC packages, sometimes experience performance degradation and/or damage due to temperature rise caused by heat generation during use. Therefore, conventionally, a thermally conductive sheet with good thermal conductivity and/or thermally conductive grease are used between the IC package and a heat-dissipating component with a heatsink to effectively transfer the heat generated by the IC package to the heatsink for dissipation. However, with the increasing performance of electronic components, their heat generation tends to increase, thus requiring the development of materials/components with superior thermal conductivity compared to previous methods.

Conventional thermally conductive sheets offer the advantage of easy disassembly and installation in terms of operation/procedure. Furthermore, in the case of thermally conductive grease, it is unaffected by the unevenness of surfaces such as the CPU and heat dissipation components, following these surfaces without creating gaps between them, thus ensuring a tight seal and low interfacial thermal resistance. However, both thermally conductive sheets and thermally conductive greases are obtained by combining thermally conductive fillers to impart thermal conductivity. In the case of thermally conductive sheets, in order to avoid hindering workability/processability during manufacturing, and in the case of thermally conductive greases, in order to avoid workability problems when applying them to heating electronic components using syringes, the upper limit of their apparent viscosity needs to be suppressed to a certain extent. Therefore, in both cases, the upper limit of the amount of thermally conductive filler is limited, resulting in the disadvantage of not achieving sufficient thermal conductivity.

Therefore, methods have been proposed for incorporating low-melting-point metals into thermally conductive pastes (Patent 1: Japanese Patent Application Publication No. 7-207160, Patent 2: Japanese Patent Application Publication No. 8-53664); and for granular materials that fix liquid metals in a three-phase composite and have a stabilizing effect (Patent 3: Japanese Patent Application Publication No. 2002-121292). However, the use of these thermally conductive materials with low-melting-point metals can contaminate parts other than the coated area, and problems such as oily leakage may occur with prolonged use. To address these issues, a method for dispersing gallium and/or gallium alloys in addition-hardening silicone has been proposed (Patent 4: Japanese Patent No. 4551074). However, this method fails to adequately meet the requirements when the composite thickness is large due to its low thermal conductivity. Furthermore, while methods for improving thermal conductivity have been proposed (Patent 5: Japanese Patent No. 4913874 and Patent 6: Japanese Patent No. 5640945), these methods are prone to generating cracks or voids during hardening, preventing the full realization of performance.

Furthermore, in conventional addition-curing silicone compounds, hydrogen from the Si-H groups of the hydrogen-cured polysiloxane sometimes desorbs due to the coexistence of water in the system memory and silane hydrogenation catalysts, such as platinum catalysts. This desorption can create hydrogen bubbles within the system, forming voids in the cured material and thus impairing thermal conductivity. Prior Art Documents Patent Documents

[Patent Document 1]: Japanese Patent Application Publication No. 7-207160 [Patent Document 2]: Japanese Patent Application Publication No. 8-53664 [Patent Document 3]: Japanese Patent Application Publication No. 2002-121292 [Patent Document 4]: Japanese Patent Publication No. 4551074 [Patent Document 5]: Japanese Patent Publication No. 4913874 [Patent Document 6]: Japanese Patent Publication No. 5640945

The problem to be solved by the invention

Therefore, the object of this invention is to provide a thermally conductive silicone composition. The material, possessing excellent thermal conductivity, is formulated in a required and sufficient amount, and said material is uniformly dispersed in particulate form within a matrix composed of resin components, and upon curing, it can form a cured product that does not produce cracks or voids. Solution to the Problem

To solve the above problems, the inventors conducted in-depth research and found that by incorporating low-melting-point gallium and/or gallium alloys, thermally conductive fillers, and palladium powder into addition-hardening silicone compounds, it is easy to obtain a compound in which the gallium and/or gallium alloys are uniformly dispersed in a particulate state. Furthermore, in the step of heating the compound to form a hardened product, the generation of cracks or voids can be suppressed. The resulting hardened product can achieve high heat dissipation performance, thus completing the present invention.

That is, the present invention provides the following curable organic polysiloxane composition and its cured form.

<1> A thermally conductive silicone composition comprising the following components: (A) an organic polysiloxane: 100 parts by weight, having a kinematic viscosity of 10 to 1,000,000 ^mm² /s at 25°C, and having two or more aliphatic unsaturated hydrocarbon groups bonded to silicon atoms in one molecule; (B) an organic hydrogen polysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule: the number of hydrogen atoms bonded to silicon atoms in the component is 0.5 to 5.0 relative to one alkenyl group in component (A); (C) one or more selected from the group consisting of gallium and gallium alloys with melting points of -20 to 70°C: 300 to 20,000 parts by weight; (D) Thermally conductive filler with an average particle size of 0.1 to 100 µm: 10 to 1000 parts by weight; (E) Platinum group metal catalyst; (F) Palladium powder; and, (G-1) Organic polysiloxane represented by the following general formula (1): 0.1 to 500 parts by weight. (In formula (1), ^R1 is independently an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms that does not have aliphatic unsaturated bonds, and ^R2 is independently an alkyl, alkenyl, or acetyl group. Additionally, a is an integer from 5 to 100, and b is an integer from 1 to 3.) <2> The thermally conductive silicone composition according to <1>, wherein component (F) is palladium powder with an average particle size of 1 to 100 nm. <3> The thermally conductive silicone composition according to <1> or <2>, wherein the amount of component (F) is 0.00001 to 1.0 parts by mass relative to 100 parts by mass of component (A). <4> The thermally conductive silicone composition according to any one of <1> to <3>, wherein component (F) is supported on a carrier other than palladium. <5> The thermally conductive silicone composition according to <4>, wherein the support is silicon dioxide. <6> The thermally conductive silicone composition according to any one of <1> to <5> further comprises, relative to 100 parts by mass of component (A), 0.1 to 100 parts by mass of a (G-2) alkoxysilane compound represented by the following general formula (2). (In formula (2), ^R3 independently represents an alkyl group having 6 to 16 carbon atoms, ^R4 independently represents an unsubstituted or substituted monovalent hydrocarbon having 1 to 8 carbon atoms, ^R5 independently represents an alkyl group having 1 to 6 carbon atoms, c is an integer of 1 to 3, d is an integer of 0 to 2, and the sum of c and d is an integer of 1 to 3.) <7> The thermally conductive silicone composition according to any one of <1> to <6> further comprises, relative to 100 parts by mass of component (A), 0.1 to 100 parts by mass of (G-3)trifluoropropyltrimethoxysilane. <8> A thermally conductive silicone composition according to any one of <1> to <7>, wherein, relative to 100 parts by mass of component (A), it further comprises 0.1 to 5 parts by mass of an (H) addition reaction control agent, selected from one or more of the group consisting of acetylene compounds, nitrogen compounds, organophosphorus compounds, oxime compounds, and organochlorine compounds. <9> A thermally conductive silicone composition according to any one of <1> to <8>, wherein component (C) is dispersed in the composition as particles of 1 to 200 µm. <10> A cured product, which is a cured product of the thermally conductive silicone composition according to any one of <1> to <9>. Effects of the Invention

The thermally conductive silicone compound of this invention, being in a grease-like state before curing, exhibits excellent workability when applied to heat-generating electronic components such as CPUs. Consequently, when pressing heat dissipation components, it can follow the surface irregularities of both, achieving a tight seal between them without gaps, thus eliminating interfacial thermal resistance. Furthermore, the heat treatment step of curing the thermally conductive silicone compound of this invention via an addition reaction not only suppresses cracking but also suppresses voids caused by hydrogen generated from dehydrogenation reactions within the system, resulting in a cured product with high heat dissipation properties.

[Thermally Conductive Silicone Composition] <(A) Organopolysiloxane> Component (A) of the composition of this invention is an organopolysiloxane having two or more aliphatic unsaturated hydrocarbon groups bonded to silicon atoms in one molecule, and is the main agent (base polymer) in the addition reaction curing system of this invention.

(A) The kinematic viscosity of component A at 25°C is in the range of 10~1,000,000 ^mm² /s, preferably 50~500,000 ^mm² /s. If the kinematic viscosity is lower than 10 ^mm² /s, the hardened material becomes brittle and prone to cracking; if the kinematic viscosity is greater than 1,000,000 ^mm² /s, the viscosity of the composition is too high, making it difficult to process. It should be noted that in this invention, the kinematic viscosity is the value measured at 25°C using an Ostwald viscometer.

The molecular structure of the organic polysiloxane of component (A) is not limited, and examples include, for example, straight chains, branched chains and straight chains with partial branches, with straight chains being particularly preferred.

(A) The number of aliphatic unsaturated hydrocarbon groups bonded to silicon atoms in the component is sufficient, preferably 2 to 10, and more preferably 2 to 5, per molecule. Examples of this aliphatic unsaturated hydrocarbon group include vinyl, allyl, 1-butenyl, and 1-hexenyl alkenyl groups, but vinyl is preferred considering ease of synthesis and cost. This aliphatic unsaturated hydrocarbon group can bond to any of the silicon atoms at the ends of the molecular chain or in the middle of the molecular chain, but to ensure good flexibility of the resulting cured material, it is preferable that it only bonds to the silicon atoms at the ends of the molecular chain.

Groups bonded to silicon atoms other than aliphatic unsaturated hydrocarbons bonded to silicon atoms include, for example, unsubstituted or substituted monovalent hydrocarbons such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, 2-phenylethyl, and 2-phenylpropyl; and halogenated alkyl groups such as chloromethyl, 3,3,3-trifluoropropyl, and 3-trichloropropyl. Furthermore, from both synthetic and economic perspectives, it is preferable that more than 90% of the group is methyl.

Preferred examples of such organopolysiloxanes include polydimethylsiloxanes end-capped with dimethylvinylsiloxy groups at both ends of the molecular chain, polydimethylsiloxanes end-capped with methyldivinylsiloxy groups at both ends of the molecular chain, and dimethylsiloxane/methylphenylsiloxane copolymers end-capped with dimethylvinylsiloxy groups at both ends of the molecular chain. The organopolysiloxane of component (A) can be used alone or in combination with two or more.

<(B) Organohydrogen Polysiloxane> Component (B) of the present invention is an organohydrogen polysiloxane having two or more hydrogen atoms bonded to silicon atoms (hereinafter referred to as "Si-H groups") in one molecule, which acts as a crosslinking agent for component (A) above. That is, the Si-H groups in component (B) undergo addition with the alkenyl groups in component (A) via a silaneation reaction through the platinum-based catalyst of component (E) described later, producing a cross-linked hardened product with a three-dimensional network structure holding crosslinks.

(B) The number of Si-H groups in component B is more than 2 per molecule, preferably 2 to 30. The molecular structure of component B is not particularly limited as long as it meets the above requirements, and can be any of the conventionally known structures such as linear, cyclic, branched, or three-dimensional network (resin-like). The number of silicon atoms (or degree of polymerization) per molecule is typically 3 to 1000, preferably 5 to 400, more preferably 10 to 300, even more preferably 10 to 100, and particularly preferably 10 to 60.

As a group bonded to silicon atoms other than the Si-H group, it is preferably an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and without aliphatic unsaturated bonds. Specific examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and groups in which some or all of the hydrogen atoms are substituted by halogen atoms such as fluorine or chlorine, for example, 3,3,3-trifluoropropyl. Among these, methyl is preferred considering ease of synthesis and cost.

Specific examples of organohydrosiloxanes as component (B) include dimethylsiloxane/methylhydrosiloxane copolymers with both ends of the molecular chain capped with dimethylhydrosiloxaneoxy groups, methylhydrosiloxane/dimethylsiloxane/diphenylsiloxane copolymers with both ends of the molecular chain capped with dimethylhydrosiloxaneoxy groups, dimethylsiloxane/methylhydrosiloxane copolymers with one end capped with dimethylhydrosiloxaneoxy and the other end capped with trimethylsiloxaneoxy, methylhydrosiloxane/dimethylsiloxane/diphenylsiloxane copolymers with one end capped with dimethylhydrosiloxaneoxy and the other end capped with trimethylsiloxaneoxy, and copolymers composed of ( _CH3 ) _2HSiO A copolymer composed of ( _CH3 ) _{3SiO 1/2 unit} and ( _CH3 )HSiO _2/2 unit and SiO _4/2 unit; _a copolymer composed of ( _CH3 ) _2HSiO 1/2 unit and (CH3)3SiO _1/2 unit and ( _CH3 ) _{HSiO 2/2} unit and ( _CH3 )2SiO 2/2 unit and SiO 4/2 unit; a copolymer composed of (CH3)2HSiO _1/2 unit and (CH3)HSiO 2/2 unit and ( _CH3 ) _{2SiO 2/2} unit and SiO _4/2 unit; a copolymer composed of ( _CH3 ) _{2HSiO 1/2} unit and SiO _{4/2 unit and (CH3)HSiO 2/2 unit} and ( _CH3) 2HSiO _1/2 unit and (CH3)2HSiO _4/2 unit and (CH3)2HSiO 1/2 unit and SiO _{4/2 unit; a copolymer composed of (CH3)2HSiO 1/2 unit and (CH3)2HSiO 2/2 unit and ( CH3} )2HSiO _2/2 unit and (CH3)2HSiO _{4 ...} Copolymers composed of ( _CH3 ) _{2HSiO 2/2} units and ( _CH3 ) _{3SiO 1/2} units; copolymers composed of ( _CH3 ) _{2HSiO 1/2} units, ( _CH3 ) _{3SiO 1/2} units, ( _C6H5 ) _{2SiO 2/2} units, ( _CH3 )HSiO _2/2 units, ( _CH3 ) _{2SiO 2/2} units, and SiO _4/2 units _, etc.

Relative to the one aliphatic unsaturated hydrocarbon group bonded to silicon atoms in component (A), the amount of component (B) is in the range of 0.5 to 5.0, preferably 0.7 to 3.0, of Si-H groups in component (B). If the amount of component (B) is below the lower limit of the above range, the grease may not harden sufficiently due to insufficient network formation; if the amount of component (B) exceeds the upper limit of the above range, the resulting thermally conductive silicone composition may become too rigid, have poor reliability, and be prone to foaming. The organohydrogen polysiloxane in component (B) can be used alone or in combination with two or more.

<(C) Gallium and/or Gallium Alloy> The (C) component of the composition of this invention is gallium and/or a gallium alloy with a melting point of -20 to 70°C. This (C) component is formulated to impart good thermal conductivity to the hardened product obtained from the composition of this invention, and the formulation of this component is characteristic of this invention.

As stated above, the melting point of component (C) needs to be in the range of -20 to 70°C. While gallium and/or gallium alloys with melting points below -20°C can be physically used for use in this invention, it is difficult to obtain gallium and/or gallium alloys with melting points below -20°C, and it is also less economical. Conversely, if the melting point exceeds 70°C, it cannot melt rapidly during the composition preparation process, resulting in poor operability. Therefore, as stated above, the melting point of component (C) is preferably in the range of -20 to 70°C. In particular, gallium and/or gallium alloys in the range of -19 to 50°C are easier to use to prepare the composition of this invention, and are therefore preferred.

The melting point of metallic gallium is 29.8℃. Other representative gallium alloys include, for example, gallium-indium alloys (e.g., Ga-In (mass ratio = 75.4:24.6, melting point = 15.7℃); gallium-tin alloys and gallium-tin-zinc alloys (e.g., Ga-Sn-Zn (mass ratio = 82:12:6, melting point = 17℃); and gallium-indium-tin alloys (e.g., Ga-In-Sn (mass ratio = 6...). 8.5:21.5:10, melting point = -19℃ or mass ratio = 62:25:13, melting point = 5.0℃ or mass ratio = 21.5:16.0:62.5, melting point = 10.7℃), gallium-indium-bismuth-tin alloy; for example Ga-In-Bi-Sn (mass ratio = 9.4:47.3:24.7:18.6, melting point = 48.0℃), etc.

Component (C) can be used alone or in combination of two or more. The liquid or solid particles of gallium and/or gallium alloy present in the uncured composition of the present invention are generally spherical, but may also include amorphous particles. Furthermore, the average particle size of the gallium and/or gallium alloy is typically 1-200 μm, preferably 5-150 μm, and even more preferably 10-100 μm. If the average particle size is too small, the viscosity of the composition is too high, resulting in a lack of ductility and thus causing problems with coating operability. Conversely, if the average particle size is too large, the composition becomes uneven, making it difficult to apply thin films to heating electronic components, etc. It should be noted that, regarding the shape and average particle size, and consequently the dispersion state in the composition, as described above, since the composition is rapidly kept at a low temperature after preparation, it can be maintained until the coating step for heat-generating electronic components, etc. It should also be noted that the average particle size was calculated by observing the composition before curing, sandwiched between two glass slides, using a VR-3000 manufactured by KEYENCE Inc. That is, 10 particles were randomly selected from images captured by this measuring instrument, their individual particle sizes were measured, and their average value was calculated.

Relative to 100 parts by mass of component (A) above, the amount of component (C) is 300 to 20,000 parts by mass, preferably 2,000 to 15,000 parts by mass, and even more preferably 3,000 to 12,000 parts by mass. If the amount is less than 300 parts by mass, the thermal conductivity becomes low, and sufficient heat dissipation performance cannot be obtained in the case of a thick composition. If the amount is greater than 20,000 parts by mass, it is difficult to form a uniform composition. In addition, due to the excessively high viscosity of the composition, it is sometimes impossible to obtain a grease-like composition with ductility.

<(D) Thermally Conductive Filler> In the composition of this invention, a thermally conductive filler (D), which is conventionally used in thermally conductive sheets or greases, is required in conjunction with component (C) (except for component (C)).

As for component (D), there are no particular limitations as long as it has good thermal conductivity; any previously known powders can be used. Examples include, for instance, aluminum powder, zinc oxide powder, alumina powder, boron nitride powder, aluminum nitride powder, silicon nitride powder, copper powder, diamond powder, nickel powder, zinc powder, stainless steel powder, and carbon powder. Furthermore, component (D) can be used alone or in combination with two or more other powders. In particular, from the viewpoint of easy availability and economy, zinc oxide powder and alumina powder are especially preferred.

The average particle size of component (D) is in the range of 0.1 to 100 µm, preferably in the range of 1 to 20 µm. If the average particle size is too small, the viscosity of the resulting composition is too high, and therefore it lacks ductility. Conversely, if the average particle size is too large, it is difficult to obtain a uniform composition. It should be noted that the average particle size is the volume average diameter [MV] of the volume benchmark measured by a Microtrac MT3300EX laser fineness analyzer (manufactured by Nikkiso Co., Ltd., Japan).

The amount of component (D) relative to 100 parts by weight of component (A) is in the range of 10 to 1000 parts by weight, preferably in the range of 50 to 500 parts by weight. If the amount of component (D) relative to 100 parts by weight of component (A) is less than 10 parts by weight, the gallium and/or gallium alloy cannot be uniformly dispersed in component (A) or in the mixture of component (A) and component (G) described later; if the amount of component (D) relative to 100 parts by weight of component (A) is more than 1000 parts by weight, the viscosity of the composition becomes high, and a grease-like composition with ductility cannot be obtained.

<(E) Platinum Group Metal Catalyst> The platinum group metal catalyst in component (E) of the present invention is a component formulated to promote the addition reaction between the aliphatic unsaturated hydrocarbons bonded to silicon atoms in component (A) and the Si-H groups in component (B) above, resulting in a three-dimensional network-like cross-linked hardened material from the present invention. However, the platinum group metal catalyst in component (E) does not contain palladium powder, which is described later in component (F).

As component (E), any known components used in conventional silicon hydrogenation reactions can be used, such as platinum metal (platinum black), chloroplatinic acid, platinum-olefin complexes, platinum-alcohol complexes, platinum coordination compounds, etc. The amount of component (E) is not particularly limited as long as it is an effective amount required to harden the composition of the invention. For example, the mass of component (A) relative to platinum atoms is usually preferably about 0.1 to 500 ppm, more preferably 1 to 200 ppm.

<(F) Palladium Powder> The (F) component of this invention is palladium powder, a compound formulated to absorb hydrogen generated within the system and suppress porosity.

From the perspective of operability and hydrogen adsorption efficiency during formulation, the average particle size of palladium powder in component (F) is preferably 1~100 nm, and preferably 5~70 nm. This average particle size is the cumulative average diameter of the volumetric standard measured using a NANOTRAC UPA-EX150 manufactured by Nikkiso Co., Ltd.

From the perspective of suppressing voids and forming heat conduction pathways, the amount of component (F) is preferably 0.00001 to 1.0 parts by mass and particularly preferably 0.0005 to 0.1 parts by mass relative to 100 parts by mass of component (A).

There are no particular restrictions on the formulation method of component (F). Component (F) can be added to the composition in its original state and dispersed. Alternatively, it can be incorporated into products on carriers such as pyrolytic silica, wet silica, crystalline silica, and molten silica. It can also be added to the composition after dispersing component (F) in a solvent. Furthermore, a paste-like mixture obtained by uniformly dispersing component (F) in an organopolysiloxane or similar material using a three-roll mill can also be added to the composition. The average particle size of the support (e.g., crystalline silicon dioxide) is the cumulative average diameter of the volumetric reference, measured using a Microtrac MT3300EX laser fineness analyzer manufactured by Nikkiso Co., Ltd. (F) Components may be used alone or in combination of two or more.

<(G-1) Surface Treatment Agent> In the present invention, a polysiloxane represented by the following general formula (1) is used as a (G-1) surface treatment agent to hydrophobize the gallium and/or gallium alloy of component (C) during the preparation of the composition, improve the wettability of component (C) with the organopolysiloxane of component (A), and uniformly disperse component (C) as particulate matter in a matrix composed of component (A).

In addition, regarding component (G-1), the thermally conductive filler, like component (D) above, also has the effect of improving the wettability of its surface and making it uniformly dispersed.

As component (G-1), it is a polysiloxane with a single end capped with hydrolyzable groups on a molecular chain represented by the following general formula (1). The kinematic viscosity of this polysiloxane at 25°C is preferably 10~10000 ^mm² /s. It should be noted that this kinematic viscosity is a value measured using an Ostwald viscometer at 25°C. (In formula (1), ^R1 independently represents an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms that does not have aliphatic unsaturated bonds, and ^R2 independently represents an alkyl, alkenyl, or acetyl group. In addition, a is an integer from 5 to 100, and b is an integer from 1 to 3.)

In the above general formula (1), ^R1 is an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms, preferably 1 to 6, and without aliphatic unsaturated bonds. Specific examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and groups in which some or all of the hydrogen atoms of these groups are substituted by halogen atoms such as fluorine or chlorine, for example, 3,3,3-trifluoropropyl. Among these, methyl is preferred in terms of ease of synthesis and cost.

As for ^R2 in the above general formula (1), for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tributyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl can be listed; alkenyl groups such as vinyl and allyl; and acetyl groups such as methyl, acetyl, and benzoyl. Among them, methyl and ethyl are particularly preferred.

The amount of component (G-1) relative to 100 parts by mass of component (A) is in the range of 0.1 to 500 parts by mass, preferably 1 to 300 parts by mass, and more preferably 10 to 250 parts by mass. If the amount is less than the lower limit of the above range, components (C) and (D) cannot be sufficiently dispersed and cannot form a homogeneous composition; if the amount exceeds the upper limit of the above range, component (A) becomes relatively less, and therefore, the resulting composition is difficult to harden. After the composition is coated on devices such as CPUs, the thermal conductivity is sometimes significantly reduced due to deviations.

<Other Components> In addition to the essential components mentioned above, the following components may also be incorporated into the curable organopolysiloxane composition of this invention as needed. <(H) Addition Reaction Control Agent> The addition reaction control agent for the (H) component of the composition of this invention is a component incorporated as needed. It is a component incorporated in a manner that inhibits the silicon hydrogenation reaction under the action of the aforementioned platinum-based catalyst at room temperature, ensuring the usable time (shelf life, service life) of the composition of this invention, and does not hinder the coating operation of heat-generating electronic components, etc.

As the (H) component, all known addition reaction control agents commonly used in addition-curing organosilicon compositions can be used. Examples include, for instance, alkynes such as 1-ethynyl-1-cyclohexanol and 3-butyn-1-ol, or various nitrogen compounds, organophosphorus compounds, oxime compounds, and organochlorine compounds.

The amount of component (H) varies depending on the amount of component (E) used above, and cannot be generalized. It only needs to be an effective amount to inhibit the hydrogenation reaction of silicon; there are no particular limitations. From the viewpoint of ensuring sufficient usability and curability of the compound, the amount of component (H) is typically about 0.1 to 5 parts by weight relative to 100 parts by weight of component (A). It should be noted that, to improve the dispersibility of component (H) in the compound, it can be used after dilution with organic solvents such as toluene, xylene, or isopropanol, if necessary. It should be noted that component (H) can be used alone or in combination with two or more components.

Furthermore, the following alkoxysilanes, which are components of (G-2), can also be formulated in the present invention. (G-2) has the following general formula (2): ^R3c _R4d Si( ^OR5 ) ⁴ _{- cd} (2) (In formula (2), ^R3 is independently an alkyl group having 6 to 16 carbon atoms, ^R4 is independently an unsubstituted or substituted monovalent alkyl group having 1 to 8 carbon atoms, ^R5 is independently an alkyl group having 1 to 6 carbon atoms, c is an integer from 1 to 3, d is an integer from 0 to 2, and the sum of c+d is an integer from 1 to 3.)

^R3 in the above general formula (2) can be, for example, hexyl, octyl, nonyl, decyl, dodecyl, tetradecyl, etc. If the number of carbon atoms is less than 6, the wettability of the above components (C) and (D) cannot be sufficiently improved; if the number of carbon atoms exceeds 16, the organosilicon of component (G-2) will solidify at room temperature, which is not only unfavorable for processing, but also reduces the low-temperature properties of the resulting composition.

Furthermore, ^R4 in the above general formula (2) can be, for example, alkyl groups such as methyl, ethyl, propyl, hexyl, and octyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl and tolyl; aralkyl groups such as 2-phenylethyl and 2-methyl-2-phenylethyl; and halogenated hydrocarbon groups such as 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, 2-(heptadecylfluorooctyl)ethyl, and p-chlorophenyl. Among these, methyl and ethyl are particularly preferred.

Furthermore, ^R5 in the above general formula (2) can be, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl. Among them, methyl and ethyl are particularly preferred.

A preferred specific example of this (G-2) composition is as follows: _C6H13Si ( _OCH3 ) ₃ C10H21Si( _OCH3 ) ₃ C12H25Si _(OCH3 ) _{3 C12H25Si} ( _OC2H5 ) ₃ C10H21( _CH3 )Si _{( OCH3} ) _{2 C10H21 ( C6H5 )} Si _{( OCH3 ) 2 C10H21 ( CH3 )} Si _{(OC2H5 ) 2 C10H21 ( CH = CH2 )} Si _{( OCH3 ) 2}

It should be noted that component (G-2) can be used alone or in combination with two or more components. Furthermore, regarding its dosage, if it is 0.1 parts by weight or more relative to 100 parts by weight of component (A), the viscosity of the mixture will easily reach the desired range; even if it exceeds 100 parts by weight, the wetting effect will not increase, which is uneconomical. Therefore, a range of 0.1 to 100 parts by weight is preferable. More preferably, it is 1 to 50 parts by weight.

Furthermore, in the composition of this invention, trifluoropropyltrimethoxysilane, as component (G-3), may be further formulated as appropriate. Regarding the amount, relative to 100 parts by weight of component (A), if it is 0.1 parts by weight or more, the viscosity of the composition is easily within the desired range; even if it exceeds 100 parts by weight, the wetting effect will not increase, which is uneconomical. Therefore, a range of 0.1 to 100 parts by weight is preferable. More preferably, it is 1 to 50 parts by weight. It should be noted that components (G-1), (G-2), and (G-3) can be used individually or in combination.

<Any other than those mentioned above> In addition to components (A) to (H) mentioned above, the composition of this invention may also contain conventionally known antioxidants such as 2,6-di-tertiary butyl-4-cresol, as needed. Further additives such as adhesives, mold release agents, dyes, pigments, flame retardants, anti-settling agents, and/or thixotropic modifiers may be added as needed.

<Viscosity of the Composition> The viscosity of the silicone composition of this invention, measured at 25°C from an operational perspective, is preferably in the range of 10–1000 Pa·s, and more preferably 30–400 Pa·s. It should be noted that this viscosity is the value measured at 25°C using a spiral viscometer PC-ITL (manufactured by MALCOM CO.,LTD.).

[Preparation of the Invention Composition] The thermally conductive silicone composition of the present invention can be obtained by a manufacturing method having the following steps, but is not limited to those described herein. The manufacturing method comprises the following steps: (i) mixing component (A), component (C), component (D), component (F), and component (G-1), and, if present, components (G-2) and (G-3), at a temperature in the range of 20-120°C and above the melting point of component (C), to obtain a homogeneous mixture (i); (ii) stopping the mixing of mixture (i) and cooling the temperature of mixture (i) to below the melting point of component (C), to obtain mixture (ii); (iii) The step of adding component (B) and component (E), component (H) if present, and other components as appropriate, to mixture (ii), and mixing under conditions lower than the melting point of component (C) to obtain a homogeneous mixture (iii).

In step (i), the liquid form of gallium and/or its alloy of component (C), the thermally conductive filler of component (D), and the palladium powder of component (F) are uniformly dispersed in a mixture of any one or both of components (A) and (G-1), and, if present, components (G-2) and (G-3).

The cooling or temperature reduction operation in step (ii) is preferably performed rapidly. In step (ii), component (C), which is uniformly dispersed in a matrix consisting of any one or a mixture of two or more of component (A), component (G-1), component (G-2) and component (G-3) if present, in liquid or solid particle form, maintains its average particle size and the dispersion state.

Step (iii) is preferably completed in the shortest possible time. At the end of step (iii), the dispersion state of the particles of component (C) has not substantially changed. Then, after step (iii) is completed, the resulting composition can be contained in a container and quickly stored in a freezer or cold storage at a temperature of approximately -30 to -10°C, preferably -25 to -15°C. Additionally, vehicles equipped with refrigeration equipment can be used for its transportation. By storing/transporting under such low-temperature conditions, the composition and dispersion state of the composition of the invention can be stably maintained, for example, even after long-term storage.

When curing the composition of the invention, it can be cured by holding it at a temperature of 80~180°C for approximately 30~240 minutes. The composition of the invention can be cured simultaneously with the application of pressure. Alternatively, post-curing can be performed after curing. The cured product of the composition of the invention can be used as a thermally conductive cured product for forming a thermally conductive layer between a heat-generating electronic component and a heat-dissipating component.

Examples The present invention will be described in more detail below with examples, but the present invention is not limited thereto. The components (A) to (H) used in the following examples and comparative examples are represented as follows. It should be noted that the viscosity is the value measured using a PC-ITL spiral viscometer (manufactured by Marcom Co., Ltd., Japan), and the kinematic viscosity is the value measured using an Ostwald viscometer (manufactured by Shibata Science Co., Ltd., Japan).

(A) Composition: Dimethyl polysiloxane with both ends capped with dimethyl vinyl silyl groups at a viscosity of 25°C as described below; (A-1) Kinematic viscosity: 100 ^mm² /s; (A-2) Kinematic viscosity: 600 ^mm² /s; (A-3) Kinematic viscosity: 30000 ^mm² /s

(B) Composition: (B-1) Organohydrosiloxane represented by the following structural formula (B-2) Organohydrosiloxanes represented by the following structural formula (B-3) Organohydrosiloxanes represented by the following structural formula

(C) Composition: (C-1) Gallium (Melting point = 29.8℃) (C-2) Ga-In alloy (mass ratio = 75.4:24.6, melting point = 15.7℃) (C-3) Ga-In-Sn alloy (mass ratio = 68.5:21.5:10, melting point = -19℃) (C-4) Ga-In-Sn alloy (mass ratio = 62:25:13, melting point = 5.0℃) (C-5) Indium (Melting point = 156.2℃) <For comparison>

(D) Composition: (D-1): Alumina powder (average particle size: 8.2µm) (D-2): Zinc oxide powder (average particle size: 1.0µm)

(E) Composition: (E-1): Dimethyl polysiloxane solution of platinum-divinyltetramethyldisiloxane complex (a compound with both ends capped with dimethylvinylsilyl groups, kinematic viscosity: 600 ^mm² /s) (platinum atom content: 1% by mass).

(F) Composition: (F-1) Palladium powder (average particle size: 5nm) (F-2) 1.0% by mass Palladium-supported crystalline silica (average particle size of palladium powder: 2nm, average particle size of crystalline silica: 5µm) (F-3) 0.5% by mass Palladium-supported dry silica (average particle size of palladium powder: 7nm, BET specific surface area of dry silica: ^130m² /g)

(G) Composition: (G-1) A single-terminated trimethoxysilyl-terminated dimethyl polysiloxane with a kinematic viscosity of 32 ^mm² /s, represented by the following structural formula. (G-2) Structural formula: _{Organosilanes} represented by _C10H21Si ( _OCH3 ) ₃ (G-3) Trifluoropropyltrimethoxysilane. It should be noted that in the preparation steps of the composition, "(G) component" means the composition that summarizes the (G-1), (G-2) and (G-3) components used in the respective examples recorded in Table 1 or Table 2.

(H) Component: (H-1)1-Ethynyl-1-cyclohexanol

[Examples 1-6, Comparative Examples 1-6] <Preparation of the Composition> The components were weighed according to the composition ratios recorded in Tables 1 and 2, and the composition was prepared as described below. Components (A), (C), (D), (F), and (G) were added to a 250 ml adjustable mixer (manufactured by THINKY CORPORATION, trade name: Awatori Rentaro). The mixture was heated to 70°C and maintained at that temperature while mixing for 5 minutes. Then, mixing was stopped, and the mixture was cooled to 25°C. Next, components (B), (E), and (H) were added to a mixture of components (A), (C), (D), (F), and (G), and mixed at 25°C until homogeneous, thereby preparing the various compositions.

<Viscosity Determination> The absolute viscosity of the compositions was determined at 25°C using a PC-1TL (10 rpm) viscometer manufactured by Marcom International Inc.

<Determination of Kinematic Viscosity> The kinematic viscosity of the compositions was measured at 25°C using an Ostwald viscometer (manufactured by Shibata Science Co., Ltd., Japan).

<Determination of Thermal Conductivity> The obtained compositions were cast into 3cm thick molds, covered with kitchen plastic wrap, and the thermal conductivity of each composition was measured using a Model QTM-500 manufactured by Kyoto Electric Industries, Ltd., Japan.

<(C) Particle Size Determination of Components> 0.1g of each of the above-obtained components was sandwiched between two glass slides. Ten particles were randomly selected from images taken using a VR-3000 camera manufactured by KEYENCE Inc., and their particle sizes were measured. Their average values were calculated.

<Determination of Thermal Resistance> The various compositions obtained above were sandwiched between 15mm × 15mm × 1mm thick Ni plates. While applying a pressure of 137.9 kPa, the plates were simultaneously heated and hardened at 150°C for 60 minutes to prepare test pieces for thermal resistance measurement. The thermal resistance was then measured using a thermal resistance meter (NETZSCH LFA447 model).

<Porosity Test> 0.1g of each composition was sandwiched between two 5×7cm glass slides, and simultaneously heated and hardened for 1 hour on a heated plate preheated to 150°C. After cooling the test slides to 25°C, the hardened material sandwiched between the slides was observed with the naked eye and under a microscope (manufactured by KEYENCE Co., Ltd.: Model VR-3000). [Evaluation] • Cracks visible to the naked eye are rated as: × • One or more circular voids with a diameter of 0.5 mm or more are visible under a microscope are rated as: × • No cracks or circular voids with a diameter of 0.5 mm or more are visible to the naked eye or under a microscope are visible as: ○

<(D) Particle Size Determination> The average particle size of the thermally conductive filler is the cumulative average diameter of the volumetric reference, measured using a Microtrac MT3300EX laser fineness analyzer manufactured by Nikkiso Co., Ltd.

<(F) Particle Size Determination> The average particle size of palladium powder was determined using the cumulative average diameter of volumetric parameters, measured with a NANOTRAC UPA-EX150 laser fineness analyzer manufactured by Nikkiso Co., Ltd. Additionally, the average particle size of the crystalline silica used as a support was determined using the cumulative average diameter of volumetric parameters, measured with a Microtrac MT3300EX laser fineness analyzer manufactured by Nikkiso Co., Ltd.

Table 1 Implementation Examples 1 2 3 4 5 6 (A)Ingredients A-1 60 40 50 70 A-2 100 80 A-3 40 60 50 20 30 (B) Ingredients B-1 6.8 5.4 B-2 7.0 6.0 4.2 1.6 3.8 B-3 7.5 2.5 2.0 (C) Components C-1 3500 C-2 6000 6000 C-3 4000 12000 C-4 7000 (D) Components D-1 200 100 100 50 50 50 D-2 50 50 50 50 50 (E) Components E-1 0.3 0.3 0.3 0.3 0.3 0.3 (F)Ingredients F-1 0.05 0.05 F-2 4 4 4 F-3 6 (G) component G-1 50 50 50 100 100 300 G-2 30 10 20 10 G-3 10 (H) component H-1 0.3 0.3 0.3 0.3 0.3 0.3 H/Vi * 1.5 1.8 1.5 0.8 1.0 1.0 Viscosity [Pa·s] 70 85 75 90 100 220 Thermal conductivity [W/mK] 5.2 6.4 6.0 6.8 6.5 7.2 (C) Particle size of the component [μm] 40 50 55 45 35 45 Thermal resistance [ ^mm² K/W] 1.2 1.2 1.5 1.3 1.1 1.2 void test 〇 〇 〇 〇 〇 〇 *; For convenience, the number of hydrogen atoms bonded to silicon in component (B), which is the aliphatic unsaturated hydrocarbon group bonded to a silicon atom relative to component (A), is denoted as H/Vi.

Table 2 Comparative example 1 2 3 4 5 6 (A)Ingredients A-1 40 50 40 100 60 A-2 100 A-3 60 50 60 40 (B) Ingredients B-1 40 15 B-2 6.0 11 0.6 5.5 7.0 B-3 4.2 twenty three (C) Components C-1 4000 C-2 6000 25000 C-3 7000 C-4 200 C-5 7000 (D) Components D-1 100 100 50 200 50 100 D-2 50 50 50 50 (E) Components E-1 0.3 0.3 0.3 0.3 0.3 0.3 (F)Ingredients F-1 0.05 0.05 F-2 4 4 F-3 6 (G) component G-1 50 50 100 50 300 100 G-2 30 20 20 50 20 G-3 10 (H) component H-1 0.3 0.3 0.3 0.3 0.3 0.3 H/Vi * 1.8 5.5 0.2 1.5 1.5 1.5 Viscosity [Pa·s] 80 75 80 8 *2 *2 Thermal conductivity [W/mK] 6.3 5.5 6.7 0.8 (C) Particle size of the component [μm] 45 40 40 100 Thermal resistance [ ^mm² K/W] 3.2 6.8 *1 25 void test × × 〇 *; For convenience, the number of hydrogen atoms bonded to silicon atoms in component (B) relative to one aliphatic unsaturated hydrocarbon group bonded to a silicon atom in component (A) is denoted as H/Vi. *1; Due to failure to harden, it cannot be determined. *2; Due to failure to obtain a homogeneous, grease-like compound, it cannot be determined.

As shown in Tables 1 and 2, the thermally conductive silicone compositions of Examples 1-6, which satisfy the requirements of this invention, yield a uniform, grease-like composition. Furthermore, component (C), acting as a thermally conductive filler, is uniformly dispersed in a particulate state, effectively suppressing cracks and voids after curing. The resulting cured product exhibits high heat dissipation performance. On the other hand, in Comparative Example 1 (which does not contain palladium powder) and Comparative Example 2 (which has an excessively high H/Vi ratio), voids induced by hydrogen generated in the system were observed. Additionally, in Comparative Example 3 (which has an excessively low H/Vi ratio), the composition failed to cure; and in Comparative Example 4 (which has a low content of component (C), sufficient heat dissipation performance could not be guaranteed. Furthermore, in Comparative Example 5, where the content of component (C) was excessive, and in Comparative Example 6, where the melting point of component (C) was excessively high, a homogeneous, grease-like composition was not obtained. [Industrial Applicability]

The thermally conductive silicone composition of this invention has good thermal conductivity and does not produce cracks and voids in the hardened material, thus achieving low thermal resistance. For example, by using it between IC packages such as CPUs and heat dissipation components, heat can be effectively removed.

without

without.

Claims (9)

A thermally conductive silicone composition comprising the following components: (A) an organic polysiloxane: 100 parts by weight, having a kinematic viscosity of 100 to 30,000 ^mm² /s at 25°C, and having two or more aliphatic unsaturated hydrocarbon groups bonded to silicon atoms in one molecule; (B) an organic hydrogen polysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule: the number of hydrogen atoms bonded to silicon atoms in the component is 0.5 to 5.0 relative to one alkenyl group in component (A); and (C) one or more selected from the group consisting of gallium and gallium alloys with melting points of -20 to 70°C: 3,000 to 12,000 parts by weight. (D) Thermally conductive filler with an average particle size of 0.1 to 100 µm: 10 to 1,000 parts by weight; (E) Platinum group metal catalyst; (F) Palladium powder with an average particle size of 1 to 100 nm; and (G-1) Organic polysiloxane represented by the following general formula (1): 0.1 to 500 parts by weight. In formula (1), ^R1 is independently an unsubstituted or substituted monovalent hydrocarbon with 1 to 10 carbon atoms that does not have aliphatic unsaturated bonds, and ^R2 is independently an alkyl, alkenyl, or acetyl group. In addition, a is an integer from 5 to 100, and b is an integer from 1 to 3. The thermally conductive silicone composition as described in claim 1, wherein, relative to 100 parts by mass of component (A), the amount of component (F) is an amount containing 0.03 to 1.0 parts by mass of palladium. The thermally conductive silicone composition as described in claim 1, wherein the (F) component is supported on a carrier other than palladium. The thermally conductive silicone composition as described in claim 3, wherein the support is silicon dioxide. The thermally conductive silicone composition as described in claim 1, wherein, relative to 100 parts by mass of component (A), it further comprises 0.1 to 100 parts by mass of (G-2) an alkoxysilane compound represented by the following general formula (2). In formula (2), ^R3 independently represents an alkyl group with 6 to 16 carbon atoms, ^R4 independently represents an unsubstituted or substituted monovalent hydrocarbon with 1 to 8 carbon atoms, ^R5 independently represents an alkyl group with 1 to 6 carbon atoms, c is an integer from 1 to 3, d is an integer from 0 to 2, and the sum of c and d is an integer from 1 to 3. The thermally conductive silicone composition as described in claim 1, wherein, relative to 100 parts by weight of component (A), it further comprises 0.1 to 100 parts by weight of (G-3) trifluoropropyltrimethoxysilane. The thermally conductive silicone composition as described in claim 1, wherein, relative to 100 parts by mass of component (A), it further comprises 0.1 to 5 parts by mass of an (H) addition reaction control agent selected from one or more of the group consisting of alkyne compounds, nitrogen compounds, organophosphorus compounds, oxime compounds and organochlorine compounds. The thermally conductive silicone composition as claimed in claim 1, wherein the (C) component is dispersed in the composition as particles of 1-200 µm. A cured material, which is a cured material of the thermally conductive silicone composition described in any one of claims 1 to 8.